So, today has me thinking about holidays and calendars and such. Obviously. And, since I'm already thinking about Greyhawk and Oerth, it's natural that my thoughts turn to the festivals of that world. Midwinter, on Oerth, is celebrated with a festival called Needfest. Looking at this festival (and the others) brings into focus one of the areas where the boxed set directly contradicts the folio. In the folio, the year was 360 days long, with each of the four festivals taking up 6 days. This was changed in the boxed set in response to the article on weather in the World of Greyhawk, where the article's author noted that a year of 364 days, with full seven-day festivals, made the two moons of Oerth move more simply. I think that I will adopt this solution, making this the only place in which I am allowing the boxed set to override the folio.
So, how would the peoples of Oerth celebrate Needfest? Well, first we'll note that the phases of the moons are fixed for the winter solstice, with Luna always being New and Celene being Full. In fact, the characteristic of all four festivals during the year is that Celene, the "Handmaiden", will be Full in the middle of the festival week. This does mean that some lycanthropes will be out wandering during every festival, so the concepts from our world of the Wild Hunt will likely have some sway in how these festivals are celebrated by many of the peoples of Oerth. We can, therefore, expect to see processions of bands of masked or costumed youths in furs wandering about, providing music of some sort (percussive, mainly, such as drums and large bells, plus singing), and demanding food and drink at the houses to which they come (like forceful carolers, perhaps). Those who give freely will get a blessing, while those who are stingy will be tormented by the wandering bands in some fashion (ranging from minor vandalism and theft to outright attacks and magical curses). Bright decorations of evergreen boughs and colorful ribbons will be placed all around settlements and outlying farmsteads. Candles and bonfires will be lit through the night (occasionally leading to tragedies, but that's the accepted price for the midwinter festivities). Songs extolling the virtues of the sun will be sung, food eaten, and drinks drunk.
Those who follow Pholtus of the Blinding Light take a dim (ha!) view of these pagan superstitions, of course, and focus almost entirely on the unconquerable, ever-returning sun without reference to the unholy, demonic lycanthrope scourge who follow the whims of the inconstant moons. St. Cuthbert's followers, on the other hand, have been slowly transforming the rites into a celebration of the wisdom of Cuthbert, adopting and reimagining the pagan celebrations of the people as celebrations of the birth of the god, all while phasing out the costumed begging/thuggery. Perhaps they encourage the caroling, however, and the giving of those alms to carolers.
The Baklunish people don't seem to have the same celebrations of midwinter. Lacking information about their calendar, I can't say for certain what goes on in the far Northwest. I'll think about it, and if I ever have any players go up there, we may find out.